JPH02214311A - Oscillating circuit for microcomputer - Google Patents

Abstract

PURPOSE:To reduce a signal leaked to the outside of a microcomputer and to reduce spurious radiation by providing a logic circuit with a high gain and a logic circuit with a low gain and applying switching control at application of power and after the stable oscillation. CONSTITUTION:The title circuit consists of a feedback amplifier comprising a crystal oscillator 1, a 1st logic circuit 4 made up of an inverter with a high gain and a 2nd logic circuit 5 made up of an inverter with a low gain, and of a phase detection control circuit 8 applying switching control to the 2nd logic circuit 5 in response to the phase of an oscillated signal 8. Then the oscillator 1, a feedback resistor 2 and a capacitor 3 are mounted externally to a CPU 10 and the logic circuits 4, 5 and the phase detection control circuit 6 are built in the inside of a CPU 10. The logic circuits 4, 5 are used at application of power to oscillate the oscillator 1 and the oscillation of the logic circuit 4 with high gain is stopped by the control circuit 6 after the stabilized oscillation and the oscillated element 1 is oscillated with the logic circuit 5 with a low gain only. As a result, the signal leaked to the outside of the CPU 10 is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oscillation circuit used as a clock pulse generator for various computer equipment using a microcomputer, and in particular to a method for eliminating signals leaking to the outside as unnecessary radiation from the oscillation circuit. This relates to a reduced oscillation circuit for a microcomputer.

[Conventional technology]

An example of an oscillation circuit conventionally used as a clock pulse generator in a microcomputer will be described with reference to FIG. This oscillation circuit, as shown in Figure 3,
A logic circuit 11 including crystal oscillators 1 and 1, a feedback resistor 2, a capacitor 3, and an inverter as a feedback amplifier.
The logic circuit 11 is built into a microcomputer (hereinafter also referred to as CPU) 10. When power is supplied to the CPU10, power is also supplied to the logic circuit 11, and the oscillator 1 starts oscillating via the feedback resistor 2 and capacitor 3, thereby oscillating at its natural frequency. It's so hot.

[Problem to be solved by the invention]

However, in such a conventional circuit, since the oscillator 1 is caused to oscillate by the logic circuit 11 with a predetermined gain, there is a problem in that it is not possible to reduce the signal leaking to the outside of the CPU 10. Ta.

The present invention has been made to solve these problems, and an object of the present invention is to provide an oscillation circuit for a microcomputer that reduces unnecessary radiation by reducing signals leaking from the oscillation circuit to the outside.

[Means to solve the problem]

In order to achieve the above object, the oscillation circuit for a microcomputer according to the present invention includes a feedback amplifier consisting of a first logic circuit with a high gain and a second logic circuit with a low gain.

The second logic circuit is switched and controlled between when the power is turned on and after the oscillation is stabilized.

[Effect]

Therefore, in the present invention, by performing oscillation with a high gain when the power is turned on, and performing oscillation with a low gain after the oscillation stabilizes, it is possible to reduce signals leaking to the outside of the microcomputer during normal operation.

[Example] Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of an oscillation circuit according to the present invention. The oscillation circuit of this embodiment includes a crystal oscillator 1, a first logic circuit 4 such as a high gain inverter, and a second logic circuit 5 such as a low gain inverter.
a feedback amplifier consisting of these first logic circuits 4. It is comprised of a phase detection control circuit 6 for switching and controlling the second logic circuit 5 in accordance with the phase of the oscillation signal 8.

However, in this example, oscillator 1. Feedback resistance 2. The capacitor 3 is externally connected to cp[Jlo, and is connected to the first logic circuit 4.
．． The second logic circuit 52 phase detection control circuit 6 is connected to the CPU1
Built-in internally. In FIG. 1, reference numeral 9 indicates each logic circuit 4, 5 sent from the phase detection control circuit 6.
The same reference numerals in the drawings indicate the same or corresponding parts.

According to the oscillation circuit configured in this way, by using the first logic circuit 4 with a high gain, the second logic circuit 5 with a low gain, and the phase detection control circuit 6 that controls them, for example, when the power is turned on, both The oscillator 1 is made to oscillate using the logic circuits 4 and 5, and after the oscillation stabilizes, the control circuit 6 stops the oscillation of the first logic circuit 4 with a high gain, and the oscillator 1 is made to oscillate using only the second logic circuit 5 with a low gain. can be made to oscillate. As a result, it is possible to reduce the amount of signals leaking to the outside of the CPU10.

FIG. 2 shows another embodiment of the present invention, and the difference from FIG. 1 is that a gate element 7 is externally attached as the first logic circuit 4 with a high gain; The control is performed using the control signal 9 of the phase detection control circuit 6. In this embodiment as well, as in FIG. 1, when the power is turned on, both logic circuits 4 and 5 are used to cause the oscillator 1 to oscillate, and after the oscillation is stabilized, the gate element 7 is turned off and the first logic circuit with a high gain is activated. By stopping the oscillation of the circuit 4, the oscillator 1 can be caused to oscillate only by the second logic circuit 5 having a low gain.

It goes without saying that the present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims.

〔Effect of the invention〕

As explained above, the present invention provides a high-gain logic circuit and a low-gain logic circuit in the oscillation circuit of a microcomputer, and switches and controls them when the power is turned on and after the oscillation is stabilized. This has the effect of reducing the amount of signals leaking to the outside and reducing unnecessary radiation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a block diagram showing an example of a conventional microcomputer oscillation circuit. . 1...Resonator, 2...Feedback resistor, 3...Capacitor, 4...First logic circuit, 5...Second logic circuit, 6...Phase detection Circuit, 7...
Gate element, 1o --- Microcomputer (CP
U).

Claims (1)

[Claims] In a microcomputer oscillation circuit that is composed of an oscillator and a logic circuit such as an inverter used as its feedback amplifier, the logic circuit is composed of a first logic circuit with a high gain and a second logic circuit with a low gain. An oscillation circuit for a microcomputer, comprising a control circuit that switches and controls the first logic circuit and the second logic circuit when power is turned on and after oscillation has stabilized.